For those of you that are running 4 CHT sensors under the plugs, what differences do you see between the cylinders?
Whats your typical temps for each cylinder with:
A: Engine warmed up sitting at idle for a minute or two.
B: Engine warmed up, cruising at 50-55 mph in fifth gear.
I don't own the car anymore, but on my old 75 with the 2270 I had a 4 channel digital CHT. This is going from memory so don't take these numbers as gospel, but I would see warmed up temps in this area:
That's not exact, but that type of ballpark. 2 is coolest, 3 is hottest, and 1 and 4 are about the same.
Cruising between 3k and 4k rpm in gears 1-4, temps remained pretty stable. They'd go up a few degrees while accelerating or climbing a hill, and then level off again while cruising or idling.
Also, below approx 60mph you'd have one set of temps that would hold steady for gears 1-4. Once you pass that 60-ish mph barrier temps start to climb and will level off around 15-20 degrees higher across the board at around 70mph, simply due to air resistance, which is why it's so important to keep the revs up in 5th gear. Take the top off above 60mph and temps go up another 10-15 degrees because you've further increased the car's air resistance.
So please, don't EVER cruise in 5th at 50-55mph. You're doing the engine a major disservice. Drive at that low of an rpm in 5th long enough, and you're virtually guaranteeing to have cracked heads or dropped valves in your future because the cooling fan isn't moving fast enough and your temps will creep up up up. 5th gear should not be used below 3k rpm, which equates to about 70mph.
Thanks for the replies, hope some more people chime in. I need to use my 4th gear more.
The reason for me asking is that I see a different pattern to my temps.
I havnt driven much this year with all four sensors yet but on my 2256 I see the #1 cylinder the hottest, followed by #2 and then 3 and 4 a few degrees lower and pretty even with eachother. I'll try to get it out soon for an extended drive and report back the temperatures I'm just waiting for my new rear brake pads to arrive.
Dual carbs, or FI? If dual carbs, then your carbs are out of balance. The more open the throttle butterfly is, the higher the head temp will be. Your 1,2 side carb is currently set for a higher idle than your 3,4 side carb. That's why your temps are off from where they should be.
I had that car for 2 years and I saw every possible result of temps during tuning. Your temp relationships are typical for carbs that aren't in sync, either because of tuning or because of a mis-adjusted linkage.
When tuned properly #3 will always be the hottest because it's furthest from the cooling fan, and #2 will always be the coolest because it's closest to the cooling fan.
This is a great reminder... but I've always wondered about the extra friction and heat caused by running at higher RPM. At what point are you defeating the purpose of running the engine fan faster?
Here it is 10min driving at 3250-3500 rpm in 5th. Maybe 80mph. It is 70 degrees today. If I drive for an hour or so #4 can hit 325 or even 350+ climbing a hill. Oil temp gets to 210. My oil pressure is around 60psi hot under load, 10-15 hot idle. Cold it is 80+
I've got itbs and FI.
I've measured my airflow on the cylinders at idle and #1 does draws the most air, then #3 and #4 are slightly below and #2 the least. The problem is that I have no way of adjusting the individual cylinders, only have idle air between the banks to adjust on at idle. And once the throttle butterflies is opened the idle air really doesnt matter much.
In the FI system I have the options of adjusting the fuel and timing of individual cylinders but I've left those options unused for now.
Coming home from Rt. 66 a number of years ago, I was driving up a very VERY long up hill stretch west of needles into about a 50 mph wind. The throttle wouldn't answer to accelerate and when I looked at the head temp. it was way over 400 degrees. Way over! I pulled over, let it cool, drove from then on in 4th gear and about 60-65 mph. The engine temp. cooled down nicely, to the usual 325-350 and stayed that way till I got on the other side of the mountain and then resumed in 5th gear. I should mention that when I stopped and pulled over to let it cool, I almost couldn't open the door to get out, the wind was so strong.
When the cyl. head temps go up, drop a gear, the higher rpm's mean the engine is working less hard and the fan speed also increases. Thanks to Joe Sharp for the advice.
Sorry for the sideways pictures, they are not rotated like that on my phone
Mine does not cool down above 4000rpms. I have to drop speed and reduce load on the motor if it starts climbing. It hasn’t gotten that hot in a while though, I had a problem of crud in my tank and fuel lines and my main jets would sometimes clog (running lean would increase temp). Since replacing all the lines and having the tank flushed and coated I haven’t had that issue or temps above 325 yet, although the season is getting warmer now...
Just spend the last 3 hours fiddling with the thottles.
Started with disconnecting the throttle cable and making sure the 1-2 (master) side was as closed as it would possibly go. Then I hooked up the throttle cable again and made sure there was no slack in the slave cable to the 3-4 side so both sides open simultaneously.
I started the engine and let it warm up for about 10 minutes at different rpms. (the neighbours love me) Then I took out the air gauge and started measuring. To start with
1 drew the most air, followed by 3 and 4 and last 2. By first adjusting the slave cable slightly and then the idle air screws I got cylinder 1,3 and 4 to draw the same amount of air, just below the 6 mark on the scale. CHT temps at idle was then around 110C (320F) for #1 and 125C (257F) for # 3 and #4.
The odd one out is still #2, when the others draw just below the 6 mark, #2 draws like 4,5-4,8, about a full scale marker lower and the temp is around 95 C or 205F.
What could cause #2 to draw that much less air? air leak between head and manifold, airleak between manifold and throttle body are the only things I can come up with....
What is your target AFR? Or do you have a screen shot of your map?
That's a pretty big difference in fueling at idle given the airflow differences. Assuming you are at lambda = 1 for cyl. 1 airflows, you'd be at about lamba = 1.3 for cyl. 2 at idle. That's certainly enough fuel to cause some additional cooling and result in those lower temperatures.
You could see lower flows if you have some valve adjust or pushrod length issues (not opening enough) or a flat cam lobe. I'd guess the cam is OK since your motor is pretty new.
Were your injectors all flow mapped or checked? I've seen some new injectors pretty far off the mark. If they haven't been tested it might be interesting to swap them between cylinders and see if the temperature mapping moves.
Good point. Totally forgot about that.
Target lambda is around 0,92 (8% more fuel than lambda 1.0) But at the moment I'm not using the lambda control function since thats not been fully mapped. Running off the VE and Ignition tables only. Screen shots below. This is only the map from the dyno. We still need to get some street fine tuning done especially when cruising.
My injectors were flowchecked and the results were at 3 bar of static pressure:
369, 369, 369 and 377 cc/minute. I'm not sure which injector is on what cylinder
but if the 377 one has ended up on cylinder 2 that could contribute to the lower temp but
its still a mystery why it would flow less air. I did set all the valves during the winter when I had the engine out.
I can try and swap the #1 and #2 cylinder injectors and see if that affects anything.
I cant get a 0,05 mm feeler gauge in so both butterflies are pretty much closed...
I spent 20 minutes this afternoon swapping the #1 and #2 injectors around, didnt have time to start up the engine and let it warm up tho, hopefully before the weekend.
Had a 40 minute drive today, starting with slower traffic and then a bit of 55 mph freeway in 4th gear before refueling after the winter and then a few minutes of 3200 rpm in fifth gear. CHT temps were around 285-290 for all cylinders except #2 that still reads in the 245-250 range.
Adjusting the throttle linkage and idle air seems to have smoothed out the temps over cylinders 1, 3 and 4 so at least a partial success. Hopefully I'll get some cruising tuning done in the next weeks and then enjoy a summer of more driving and less wrenching.
On the way home we stopped at a local landmark over some 17th century field marshal and snapped a few photos. Its been so cold this spring that the grass has barlely turned green yet. First day this year with temps above 70 F.
After reading through this and your struggles to get the air flow balanced for each cylinder.
Do your throttle bodies not have an air bypass screw for each cylinder?
This is benn the standard on carbs for years and I have not seen a throttle body that did not have balance screws. I can't say that I have seen a lot of throttle bodies up close but I have seen and adjusted a few.
What brand and model of throttle bodies do you have?
At least the cylinder that is different is running cooler and not hotter that the others.
No they only have one air bleed screw for each pair, I didnt know this when I bought them or I might have gotten something else.
Their description says there is a vacuum balance tube between the cylinders, if there is and it is open there should not be any flow difference at idle.
But then I am not sure what they are describing r what its function is.
Yes I'm not sure there's any fault with the throttle body.
Might be the cylinder or valve train, guess I need to make a compression check or leakdown test. Its just such a bother since the space is sooooo tight I'll have to take the throttle bodies and manifolds out.
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